MPEG-2 Video Decoder systems often employ external memory, for example, 2 MB or more of external memory, which is generally implemented using DRAM or SDRAM technology. External memory is used for various data areas, or buffers such as frame buffers.
In practice, the use of the MPEG-2 Video Decoder is limited to 2 MB of external memory in order to minimize cost of the end product. Therefore, it is of great importance for the decoder to perform all of its functions within this limitation. Of particular importance is enabling output for both the European markets which utilize the PAL standard which uses 576 video scan lines and the U.S. market which utilizes the NTSC standard of 480 video scan lines.
The MPEG-decompressed video data buffers, also called frame buffers, consume the largest part of External DRAM, therefore they are the prime candidate for memory reduction/compression. Because the frame buffers contain final pixel display and MPEG reference data, the reduction technique must retain high video fidelity in the frame buffers.
Another obstacle faced in video compression/decompression is being able to transform pictures between different sized screens. For example, a motion picture screen is in a 16:9 format, while a television screen is in a 4:3 format. As a result, a method must be provided to convert between 16:9 and 4:3 form factors.
Thus, a need exists for providing an MPEG2 compliant decoder that enables both the PAL and NTSC standards, enables changing format or form factor, and does so within 2 MB of DRAM.